Percutaneous electrical therapy system with electrode position maintenance

ABSTRACT

A percutaneous electrical therapy system with electrode position maintenance. In one embodiment, the system includes a control unit; an electrode electrically connectable to the control unit, the electrode having a sharp point at a distal end adapted to be inserted into a patient&#39;s tissue; and an inserted electrode holding mechanism adapted to hold the electrode in place after insertion of the sharp point of the electrode into the patient&#39;s tissue. In another embodiment, a method of providing electrical therapy can include inserting an electrode into a patient; using an inserted electrode holding mechanism to hold the inserted electrode in place in the patient; and applying an electrical signal to the electrode from a control unit.

BACKGROUND OF THE INVENTION

This invention relates generally to percutaneous electrical therapysystems for medical use. In particular, the invention relates to aholding mechanism for holding a percutaneous electrode in place afterinsertion.

Electrical therapy has long been used in medicine to treat pain andother conditions. For example, transcutaneous electrical nervestimulation (TENS) systems deliver electrical energy through electrodepatches placed on the surface of a patient's skin to treat pain intissue beneath and around the location of the patches. The efficacy ofTENS systems in alleviating pain is questionable at best, however.

More recently, a technique in which electrodes are placed through thepatient's skin into the target tissue has been proposed. PercutaneousNeuromodulation Therapy (“PNT”) (also sometimes called PercutaneousElectrical Nerve Stimulation or “PENS”) using percutaneously placedelectrodes achieves significantly better pain relief results than TENStreatments using skin surface electrodes. This therapy is described inGhoname et al., “Percutaneous Electrical Nerve Stimulation for Low BackPain,” JAMA 281:818-23 (1999); Ghoname et al., “The Effect of StimulusFrequency on the Analgesic Response to Percutaneous Electrical NerveStimulation in Patients with Chronic Low Back Pain,” Anesth. Analg.88:841-6 (1999); Ahmed et al., “Percutaneous Electrical NerveStimulation (PENS): A Complementary Therapy for the Management of PainSecondary to Bony Metastasis,” Clinical Journal of Pain 14:320-3 (1998);and Ahmed et al., “Percutaneous Electrical Nerve Stimulation: AnAlternative to Antiviral Drugs for Herpes Zoster,” Anesth. Analg.87:911-4 (1998). The contents of these references are incorporatedherein by reference.

Thus far, PNT practitioners have used percutaneously placed acupunctureneedles attached to waveform generators via cables and alligator clipsto deliver the therapy to the patient. This arrangement and design ofelectrodes and generator is far from optimal. For example,percutaneously placed electrodes can move or back out of position inresponse, e.g., to muscle contractions in the patient or a pulling forcefrom an attached electrical cable. The position of the electrode's pointcan affect the efficacy of the treatment. It is therefore an object ofthis invention to provide a holding mechanism for percutaneouselectrodes.

It is a further object of this invention to provide a percutaneouselectrical therapy system having electrodes and electrode assembliesthat are safe, efficacious, inexpensive and easy to use.

Other objects of the invention will be apparent from the description ofthe preferred embodiments.

SUMMARY OF THE INVENTION

The invention is a percutaneous electrical therapy system with electrodeposition maintenance. In a preferred embodiment, the system includes acontrol unit; an electrode electrically connectable to the control unit,the electrode having a sharp point at a distal end adapted to beinserted into a patient's tissue; and an inserted electrode holdingmechanism adapted to hold the electrode in place after insertion of thesharp point of the electrode into the patient's tissue. The insertedelectrode holding mechanism may include an electrode handle attached tothe electrode and adapted to be exterior to the patient's tissue afterinsertion of the sharp point into the patient's tissue.

The inserted electrode holding mechanism may also include a holdingelement adapted to be attached to the patient and to the electrode, suchas a patch adapted to mechanically interact with at least a portion ofthe electrode. In some embodiments, the patch may have an aperture, withthe inserted electrode holding mechanism also having an electrode handleattached to the electrode and adapted to mechanically interact with thepatch aperture. The system may also include an introducer adapted toinsert the electrode through the patch aperture and to cause theelectrode handle and the patch aperture to mechanically interact.

In some embodiments, the system includes an electrode assembly of whichthe inserted electrode holding mechanism is a part, the electrode andthe holding element, the electrode assembly being operable to insert theelectrode into the patient's tissue and being adapted to attach to thepatient. The electrode assembly may have a movable actuator adapted tomove the electrode from an uninserted position to an inserted position,with the inserted electrode holding mechanism including an actuatorholding mechanism adapted to hold the actuator in place when theelectrode is in its inserted position. The system may also have anactuator tool adapted to move the actuator and the electrode from theuninserted position to the inserted position. The actuator tool may befurther adapted to move the actuator and the electrode from the insertedposition to the uninserted position.

The system may include a conductor connecting the electrode and thecontrol unit, wherein the inserted electrode holding mechanism isfurther adapted to provide strain relief to the electrode.

The invention is also a method of providing electrical therapy, themethod including the steps of inserting an electrode into a patient;using an inserted electrode holding mechanism to hold the insertedelectrode in place in the patient; and applying an electrical signal tothe electrode from a control unit. In some embodiments, the insertedelectrode holding mechanism has a holding element, with the methodfurther including the step of attaching the holding element to thepatient. The holding element may be a patch, with the using stepincluding the step of mechanically interacting at least a portion of theelectrode with the patch. The holding element may also be a housing, theinserting step including the step of moving the electrode within thehousing. The inserting step may also include the step of moving anactuator within the housing, with the using step including the step ofmechanically interacting the actuator with the housing to hold theinserted electrode in place in the patient.

The invention is described in further detail below with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-E are schematic renderings of a percutaneous electrical therapysystem according to another embodiment of this invention.

FIG. 1A shows a percutaneous electrical therapy system with electrodeand sharp point protection assemblies wherein the electrode is in anundeployed and uninserted state.

FIG. 1B shows the percutaneous electrical therapy system of FIG. 1Aduring deployment, but prior to insertion, of the electrode.

FIG. 1C shows the percutaneous electrical therapy system of FIG. 1A withthe electrode in a deployed and inserted state.

FIG. 1D shows the percutaneous electrical therapy system of FIG. 1Aduring undeployment of the electrode.

FIG. 1E shows the percutaneous electrical therapy system of FIG. 1Aafter the electrode has been undeployed.

FIG. 2 shows an electrode montage for use in percutaneousneuromodulation therapy to treat low back pain.

FIG. 3 is an exploded sectional view of an electrode and sharp pointprotection assembly according to yet another embodiment of thisinvention.

FIG. 4 is a partially exploded elevational view of the embodiment ofFIG. 3.

FIG. 5 is an elevational view of the embodiment of FIG. 3 showing theelectrode and sharp point protection assemblies and an actuator tool.

FIG. 6 is a sectional view of the embodiment of FIG. 3 showing theelectrode and sharp point protection assemblies and an actuator tool.

FIG. 7 is a sectional view of the embodiment of FIG. 3 showing theactuator tool in engagement with the electrode and sharp pointprotection assemblies prior to insertion of the electrode into apatient's tissue.

FIG. 8 is a sectional view of the embodiment of FIG. 3 with theelectrode in its deployed and inserted state.

FIG. 9 shows a montage for using the embodiment of FIG. 3 to treat lowback pain with the electrodes in a partially deployed but uninsertedstate.

FIG. 10 shows the electrode montage of FIG. 9 at the beginning of theelectrode insertion step.

FIG. 11 shows the electrode montage of FIG. 9 with the electrodesdeployed, inserted and attached to a control unit to provide electricaltherapy to the patient.

FIG.12 is an exploded view of an electrode introducer and sharp pointprotection assembly of yet another embodiment of this invention.

FIG. 13 is a partial sectional view of the introducer and sharp pointprotection assembly of FIG. 12.

FIG. 14 is a sectional view of the introducer and sharp point protectionassembly of FIG. 12.

FIG. 15 is an elevational view of gear assemblies of the introducer andsharp point protection assembly of FIG. 12.

FIG. 16 shows part of the electrode assembly of the embodiment of FIGS.12-15 in a montage used for treating low back pain using PNT.

FIG. 17 is an elevational view showing the introducer of FIG. 12 in theprocess of deploying an electrode.

FIG. 18 is a sectional view showing the introducer of FIG. 12 in theprocess of deploying an electrode, prior to insertion of the electrode.

FIG. 19 is a sectional view showing the introducer of FIG. 12 in theprocess of deploying an electrode, during insertion of the electrode.

FIG. 20 is a sectional view showing the introducer of FIG. 12 in theprocess of deploying an electrode, also during insertion of theelectrode.

FIG. 21 is a sectional view of an inserted electrode assembly of theembodiment of FIGS. 12-15.

FIG. 22 is a partial sectional view of an electrode remover and sharppoint protection assembly according to yet another embodiment of theinvention prior to removal of an electrode.

FIG.23 is a partial sectional view of the electrode remover and sharppoint protection assembly of FIG. 22 partially actuated but prior toremoval of an electrode.

FIG. 24 is a partial sectional view of the electrode remover and sharppoint protection assembly of FIG. 22 partially actuated but prior toremoval of an electrode.

FIG. 25 is a partial sectional view of the electrode remover and sharppoint protection assembly of FIG. 22 partially actuated and engaged withan electrode but prior to removal of the electrode.

FIG. 26 is a partial sectional view of the electrode remover and sharppoint protection assembly of FIG. 22 during removal of an electrode.

FIG. 27 is a partial sectional view of the electrode remover and sharppoint protection assembly of FIG. 22 after removal of an electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Percutaneous electrical therapy systems, such as PNT systems, deliverelectric current to a region of a patient's tissue through electrodesthat pierce the skin covering the tissue. The electric current isgenerated by a control unit external to the patient and typically hasparticular waveform characteristics such as frequency, amplitude andpulse width. Depending on the treatment or therapy being delivered,there may be one electrode containing both a cathode and an anode or aplurality of electrodes with at least one serving as a cathode and atleast one serving as an anode.

The electrode has a sharp point not only to facilitate insertion throughthe patient's skin, but also to enhance local current density duringtreatment. The placement, depth and location of the electrode's point istherefore an important aspect of the therapy. Once placed, it isimportant that the electrode not move, back out or become completelydislodged. This invention therefore provides an inserted electrodeholding mechanism for use with a percutaneous electrical therapy system.

FIGS. 1A-E are block diagrams of one embodiment of our percutaneouselectrical therapy system and electrode invention. A control unit 10 isconnected to an electrode 12 within an electrode assembly 13 via aconductor 16. For use with PNT, control unit 10 preferably supplies acurrent-regulated and current-balanced waveform with an amplitude of upto approximately 20 mA, frequency between approximately 4 Hz and 50 Hz,and pulse width of between approximately 50 μsec and 1 msec. Otherelectrical waveforms having other parameters may be used, of course,depending on the therapy to be provided. Also, while FIGS. 1A-E showonly one electrode connected to the control unit, it should beunderstood that a plurality of electrodes may be connected to a singlecontrol unit, as called for by the desired electrical stimulationtreatment.

FIG. 1A shows the electrode assembly pre-deployment. To begindeployment, distal face 21 of housing 18 is placed against the patient'sskin 22, as shown in FIG. 1B and held in place, preferably withadhesive. The system includes an electrode actuator 19 that enablesdeployment and insertion of the sharp point 20 of electrode 12 throughthe patient's skin 22 into the underlying tissue through an aperture 24in housing 18, as shown in FIG. 1C. Actuator 19 has an interference fitwith housing 18. Since housing is fixed on the patient's skin thisinterference fit provides friction requiring a minimum force to moveactuator 19 with respect to housing 18. This interference fit will keepactivator 19—and therefore electrode 12—in place after electrode point20 has been placed at the desired location. The combination of thehousing's attachment to the patient and the activator's fixed positionwith respect to the housing constitutes the electrode holding mechanismof this embodiment.

Actuator may have an optional limit stop element 23 that cooperates witha limit stop area 17 of housing 18 to limit distal movement of actuator19, thereby controlling depth of insertion of electrode 12. In apreferred embodiment of the invention, for example, where the electricalstimulation system is used to provide percutaneous neuromodulationtherapy, the predetermined electrode depth is approximately 3 cm.,although other electrode depths may be used depending on theapplication. The control unit 10 may then provide the appropriatetherapy to the patient through electrode 12 and any other electrodesconnected to it.

During undeployment, actuator 19 is used to draw electrode 12 backproximally into housing 18. While FIGS. 1A-E show the electrodeconnected to the control unit prior to deployment and insertion of theelectrode into the patient's skin, the connection between the controlunit and the electrode could be made during deployment or afterinsertion. Also, while FIGS. 1A-E show only one electrode connected tothe control unit, it should be understood that a plurality of electrodesmay be connected to a single control unit, as called for by the desiredelectrical stimulation treatment.

To use the percutaneous electrical therapy systems of FIGS. 1A-E totreat a patient, one or more electrodes are inserted through thepatient's skin into the underlying tissue. As an example, to treat lowback pain using PNT with unipolar electrodes, an array or montage suchas that shown in FIG. 2 may be used. The “T12”-“S1” designations referto the patient's vertebrae. The control unit or generator suppliescurrent pulses between pairs of electrodes for durations of a fewminutes to several hours, preferably delivering the current-regulatedwaveform described above. Thirty minute treatments are recommended inthe Ghoname et al. low back pain treatment articles.

During deployment and treatment, the electrode assembly and other partsof the system perform other functions in addition to holding theelectrode in place. For example, in the embodiment of FIGS. 1A-E,aperture 24, distal face 21 and the interaction of actuator 19 andhousing 18 cooperate as an electrode angle of entry controller tocontrol the electrode's entry angle during insertion of the sharp pointof the electrode into the patient's tissue. Also, housing 18 providessharp point protection for the patient's caregiver or other bystanderbefore, during and after electrode insertion and electrical therapy.

Additional optional details of the electrode assembly may be found inthe following concurrently filed and commonly owned U.S. patentapplications, the disclosures of which are incorporated herein byreference: Bishay et al., “Percutaneous Electrical Therapy System WithElectrode Entry Angle Control;” Leonard et al., “Percutaneous ElectricalTherapy System Providing Electrode Axial Support;” Leonard et al,“Percutaneous Electrical Therapy System With Electrode Depth Control;”Leonard et al., “Electrode Introducer For A Percutaneous ElectricalTherapy System;” Bishay et al, “Percutaneous Electrical Therapy SystemFor Minimizing Electrode Insertion Discomfort;” Bishay et al.,“Electrode Assembly For A Percutaneous Electrical Therapy System;”Leonard et al., “Electrode Remover For A Percutaneous Electrical TherapySystem;” and Bishay et al, “Percutaneous Electrical Therapy System WithSharp Point Protection.”

FIGS. 3-11 show another embodiment of this invention. An electrodeassembly 30 includes a base 32, an electrode 34, and a plunger oractuator 36. Base 32 has a flange or flared end 44 that is adapted tomake contact with a patient's skin. Base 32 may be formed from anysuitable polymer or metal, such as a high density polyethylene (HDPE).Base 32 is preferably opaque so that the electrode cannot be seen by aneedle-shy patient.

Actuator 36 fits within a housing portion 40 of base 32 in a slidablearrangement. A locking assembly is operable to prevent relative movementbetween actuator 36 and housing 40 of base 32. In this embodiment, thelocking assembly of actuator 36 has integrally-formed resilient detents48 on its exterior cylindrical surface. In the undeployed state ofelectrode assembly 30, detents 48 mate with a corresponding openings 50in base 32 to hold actuator 36 and base 32 in place with respect to eachother to prevent electrode 34 from moving outside of the protectivehousing 40 of base 32 and thereby providing sharp point protection.Mechanisms other than the detent and opening arrangement shown here maybe used to hold the actuator and base in place may be used withoutdeparting from the invention.

In this embodiment, electrode 34 is preferably a 3 cm. long 32 gaugestainless steel needle. Other sizes and materials may be used forelectrode 34, of course, without departing from the scope of theinvention. Actuator 36 is preferably formed from HDPE as well, althoughother suitable materials may be used.

Electrode 34 has a larger-diameter handle 52 at its proximal end. Handle52 fits within a channel 54 formed within actuator 36. Channel 54 has anarrow opening 56 at its distal end whose diameter is slightly largerthan the diameter of electrode 34 but narrower than the diameter ofhandle 52 to hold electrode 34 in place within actuator 36 after initialmanufacture and assembly. As shown in FIG. 6, in an undeployed state thesharp point 38 of electrode 34 is disposed within housing portion 40 ofbase 32, specifically, within a narrow channel 42 of the housing 40.

To deploy one or more electrode assemblies on a patient in order toprovide electrical stimulation therapy (such as PNT), the distal surface46 of flange portion 44 of base 32 is mounted on the desired site on thepatient's skin, preferably with a compressible adhesive pad (not shown)surrounding a ring 43 extending downward from surface 46 around anaperture 41 formed at the distal end of channel 42, although other meansof attaching base 32 to the patient may be used as appropriate.

An electrical connector and actuator tool 60 is used to insert theelectrode and connect the electrode electrically with a control unit 62.When the distal end of actuator tool 60 is placed against the proximalends of base 32 and actuator 36, the exposed proximal end 64 ofelectrode handle 52 makes electrical contact with a contact surface 66within actuator tool 60. Contact surface 66, in turn, is electricallyconnected to the control unit 62 via a cable or other conductor 68.

Actuator tool 60 has two oppositely disposed pegs 70 extending outwardfrom the distal portion of its cylindrically surface. Pegs 70 mate withtwo corresponding slots 72 in actuator 36 and with two correspondinggrooves 74 in base 32. (The second slot 72 and second groove 74 are eachopposite the slot 72 and groove 74, respectively, shown in FIGS. 3 and4.) When connecting actuator tool 60 to electrode assembly 30, pegs 70move along longitudinal portions 76 of slots 72 and along longitudinalportions 78 of grooves 74. Concurrently, exposed distal end 64 ofelectrode handle 52 begins to make sliding contact with contact surface66 of actuator tool 60 to create the electrical connection betweenactuator tool 60 and electrode 32.

Clockwise rotation (looking down on the assembly) of actuator tool 60after pegs 70 reach the end of longitudinal portions 76 and 78 movespegs 70 into short circumferential portions 80 and 82, respectively, ofslots 72 and grooves 74. The length of circumferential portions 80 ofslots 72 is less than the length of circumferential portions 82 ofgrooves 74. Continued movement of pegs 70 along circumferential portions82 will therefore move pegs 70 against the ends 81 of circumferentialslots 80. Further clockwise rotation of actuator tool 60 will causeactuator 36 to rotate clockwise as well, thereby moving detents 48 outof openings 50 and allowing the electrode 34 and actuator 36 to movewith respect to base 32.

Second longitudinal portions 84 of grooves 74 are formed in base 32 atthe end of circumferential portions 82. Movement of pegs 70 distallyalong longitudinal portions 84 pushes pegs 70 against the distal edgesof circumferential slot portions 80, thereby moving actuator 36 andelectrode 34 distally toward the patient's skin 22.

As it moves, electrode 34 passes through channel 42, and the sharp pointof electrode 34 moves out through aperture 41. Channel 42 and actuator36 provide axial support to electrode 34 during this forward movementand also, along with the support provided by flange 44, provide entryangle guidance to the electrode. In addition, downward pressure on thepatient's skin during electrode deployment compresses the compressibleadhesive pad and presses ring 43 against the patient's skin 22, whichhelps ease electrode entry through the skin and also lessens theinsertion pain experienced by the patient.

Distal movement of the electrode and its actuator within base 32continues until the distal surface 86 of a cylindrical cap portion 92 ofactuator tool 60 meets an annular surface 88 of housing 40. At thispoint, sharp point 38 of electrode 34 has extended a predetermined depthinto the tissue underlying the patient's skin. In the preferredembodiment, this predetermined depth is approximately 3 cm., althoughother electrode depths may be desired depending on the treatment to beperformed. An interference fit between the inner surface of channel 42and the outer surface 55 of channel 52 performs this function.

Electrical stimulation treatment may begin once the electrodes have beendeployed and inserted. Control unit 62 supplies stimulation current tothe electrodes, e.g., in the manner described in the Ghoname et al.articles. The electrical waveform provided by the control unit dependson the application. For example, in an embodiment of a system providingpercutaneous neuromodulation therapy, control unit 62 would preferablyprovide a current-regulated and current-balanced waveform with anamplitude of up to approximately 20 mA, frequency between approximately4 Hz and 50 Hz, and pulse width of between approximately 50 μsec and 1msec.

The interaction of actuator tool 60 and base 32 provides stability toelectrode 34 and its electrical connection to the control unit duringtreatment by holding the electrode in place, by providing strain relieffor tugging forces on cable 68, and by providing a robust mechanicalconnection. It should also be noted that the sharp point of theelectrode is not exposed to the operator or to any other bystander atany point during deployment and use of the electrode assembly.

After treatment has been completed, the electrode may be removed fromthe patient. To do so, actuator tool 60 is moved proximally away fromthe patient. As pegs 70 move proximally along longitudinal portions 84of grooves 74, pegs 70 push against proximal edges of the actuator'scircumferential slot portions 80, thereby moving actuator 36 andelectrode 34 proximally as well. When pegs reach the proximal end oflongitudinal groove portions 84, the sharp end 38 of electrode 34 is outof the patient and safely inside housing 40 of base 32. Counterclockwisemovement of actuator tool 60 moves pegs along circumferential portions80 and 82 of slot 72 and groove 74, respectively. Since, as discussedabove, circumferential portion 80 is shorter than circumferentialportion 82, this counterclockwise movement will turn actuator 36counterclockwise.

At the limit of the counterclockwise movement, detents 48 move back intoopenings 50 to prevent further movement of the electrode and actuatorwith respect to base 32. Further distal movement of actuator tool 60moves pegs 70 distally along longitudinal portions 76 and 78 of slot 72and groove 74, respectively, to disconnect actuator tool 60 fromelectrode assembly 30. Base 32 can then be removed from the patient.

FIGS. 9-11 show the use of the electrode and inserted electrode holdingmechanism of FIGS. 3-8 to treat low back pain using PNT. As shown inFIG. 9, ten electrode assemblies 30 a-j are arranged in a montage on thepatient's back and attached with adhesive. Next, ten actuator tools 60a-j are attached to the ten electrode assemblies 30 a-j. In thisexample, prior to deployment the actuator tools are mounted on anactuator tool tray 61 that provides electrical communication to acontrol unit 62 via cable 69. The actuator tools electrically connectwith tool tray 61, and thereby to cable 69 and control unit 62, viaindividual cables 68 a-j. It should be understood that the tool tray 61and its electrical connection scheme play no part in the inventionclaimed in the present application. FIG. 10 shows the beginning of theelectrode insertion process.

Once each electrode assembly has been actuated by its respectiveactuator tool to insert an electrode into the patient's tissue (as shownin FIG. 11), control unit 62 provides electrical signals to treat thepatient. Preferably, half the electrodes (e.g., assemblies 30 b, 30 d,30 g, 30 h and 30 i) are treated as anodes, and the other half ascathodes. In the preferred embodiment, control unit 62 would provide acurrent-regulated and current-balanced waveform with an amplitude of upto approximately 20 mA, frequency between approximately 4 Hz and 50 Hz,and pulse width of between approximately 50 μsec and 1 msec. to treatthe patient's low back pain using PNT.

Another embodiment of the invention is shown in FIGS. 12-27. In thisembodiment, an electrode introducer and an electrode remover cooperateto connect and disconnect an electrode with an electrode holdingmechanism.

A preferred embodiment of an electrode introducer 100 is shown in FIGS.12-15 and 18-20. In this embodiment, introducer 100 is designed toinsert multiple electrodes. It should be understood that the principlesof this invention could be applied to an introducer designed to hold andinsert any number of electrodes.

Twelve electrodes 102 are disposed within a magazine 103 rotatablymounted within a housing 104. In this embodiment, housing 104 is atwo-part injection molded polystyrene assembly. As seen best in FIG. 13,magazine 103 rotates about a hub 105 mounted on supports formed inhousing 104. A leaf spring 106 mates with one of twelve radial grooves108 formed in magazine 103 to form a twelve-position ratchet mechanismfor rotatable magazine 103 in housing 104.

Magazine 103 has twelve electrode chambers 115 arranged radially abouthub 105. When introducer 100 is completely full, each chamber 115contains one electrode 102. The diameter of upper portion 118 of chamber115 is sized to form an interference fit with the wider portions 112 and114 of electrode handle portion 107 of electrode 102. Lower wide portion114 of electrode 102 is formed from a compressible material. Thediameter of lower portion 119 of chamber 115 is slightly larger so thatthere is no interference fit between chamber portion 119 and electrodehandle 107, for reasons explained below. Each time leaf spring 106 iswithin a groove 108, the opening 106 of a magazine chamber 115 is linedup with the aperture 117 of introducer 100, as shown in FIGS. 13 and 14.

A slide member 109 is disposed on a rail 110 formed in housing 104.Extending longitudinally downward from slide member 109 is a drive rod111, and extending longitudinally upward from slide member 109 is a gearrack 120. The teeth of gear rack 120 cooperate with teeth on arotational gear 122 mounted about a shaft 124 extending into a shaftmount 126 formed in housing 104. A second set of teeth are mounted on asmaller diameter rotational gear 128 (shown more clearly in FIG. 15)which is also mounted about shaft 124. Gears 122 and 128 rotate togetherabout shaft 124.

The teeth of smaller diameter gear 128 mesh with the teeth of a secondgear rack 130 extending from a longitudinally-movable actuator 132. Aspring 134 mounted between actuator 132 and a spring platform 136 biasesactuator 132 away from housing 104.

To deploy the electrode assembly of this embodiment, a flexible andcompressible annular patch 140 is placed on the patient's skin at thedesired site, preferably with adhesive (not shown). For example, totreat low back pain using PNT, the arrangement or montage shown in FIG.16 may be used. In this montage, five electrodes serve as cathodes andfive serve as anodes.

As shown in FIGS. 18 and 19, patch 140 has an annular rigid member 141disposed in its center and extending upwardly from it. Rigid member 141has a smaller diameter opening 142 leading to a larger diameter opening144. The diameter of opening 142 is slightly smaller than the lower wideportion 114 of the handle portion 107 of electrode 102 and slightlylarger than the diameter of the central portion 113 of handle portion107 of electrode 102.

After the patch 140 is in place, the distal end of introducer 100 isplaced against patch 140 so that introducer aperture 117 surrounds theupwardly extending portion of rigid patch member 141, as shown in FIG.17. This interaction aligns the opening 116 of one of the introducer'smagazine chambers 115 with the opening 142 of rigid member 141 and helpscontrol the electrode's angle of entry, as shown in FIG. 18. Downwardpressure on introducer 100 compresses patch 140, thereby causing theupper surface of rigid member 141 to engage a lower surface of magazine103 and pressing rigid member 141 downward into the patient's skin 22.This pressure on the patient's skin around the insertion site minimizesthe pain of insertion of the electrode.

Depressing actuator 132 moves gear rack 130 distally, which causes gears128 and 122 to rotate. Because of the relative diameters and relativetooth counts of gears 128 and 122, gear rack 120 moves longitudinally amuch greater distance than the corresponding longitudinal movement ofgear rack 130. This feature enables the electrode to be inserted itsrequired distance into the patient's skin using only a comparativelysmall movement of the operator's thumb. Distal movement of gear rack 120is guided by the movement of slide member 109 along rail 110.

As slide member 109 moves distally, drive rod 111 moves into a magazinechamber 115 until the distal end of drive rod 111 engages the topsurface of the electrode's handle portion 107. As shown in FIG. 19,further distal movement of drive rod 111 pushes electrode 102 downwardso that sharp point 108 of electrode 102 leaves the introducer housingand enters the patient's skin 22 and the tissue beneath the skin.Chamber 115 provides axial stability to the electrode 102 duringinsertion.

When the top portion 112 of electrode handle portion 107 leaves thesmaller diameter portion 118 of magazine chamber 115, it enters thelarger diameter portion 119 of chamber 115. At this point (shown in FIG.20), because the diameter of chamber portion 119 is wider than thediameter of the electrode handle 107, the electrode is no longerattached to introducer 100.

Continued downward movement of actuator 132 and drive rod 111 pushes thelower larger diameter portion 114 of electrode handle 107 through thesmaller diameter portion 142 of rigid member 141 by compressing handleportion 114. Further downward movement pushes handle portion 114 intothe larger diameter portion 144 of rigid member 141 so that the rigidmember's smaller diameter portion lies between the larger diameterportions 112 and 114 of the electrode handle 107. This interaction holdsthe electrode in place in the patient's tissue and helps provides depthcontrol for electrode insertion. In this embodiment, the preferred depthof the electrode's sharp point 108 is approximately 3 cm., althoughother electrode depths may be desired depending on the treatment to beperformed. Slider member 109 also acts as a limit stop at this pointwhen it engages the limit stop area 145 of housing 104, thereby alsocontrolling electrode insertion depth.

Magazine 103 is rotated to a new insertion position and placed againstan empty patch 140 after insertion of each electrode until allelectrodes have been deployed and inserted. A suitable electricalconnector 148 such as an alligator clip is electrically connected toelectrode 102 through an aperture (not shown) formed in the upper largerdiameter portion 112 of electrode handle 107 to provide electricalcommunication between a control unit 150 and electrode 102 via a cableor other conductor 149, as shown in FIG. 21. Patch 140 provides strainrelief for electrode 102 by preventing tugging forces on cable 149 fromdislodging the electrode from the patient, thereby helping keep theelectrode in place.

Control unit 150 supplies stimulation current to the electrodes, e.g.,in the manner described in the Ghoname et al. articles. Once again, theelectrical waveform provided by the control unit depends on theapplication. For example, in an embodiment of a system providingpercutaneous neuromodulation therapy, control unit 150 would preferablyprovide a current-regulated and current-balanced waveform with anamplitude of up to approximately 20 mA, frequency between approximately4 Hz and 50 Hz, and pulse width of between approximately 50 μsec and 1msec.

In an alternative embodiment, the lower wide portion of the electrodehandle is formed from a rigid material and has rounded camming edges.The central annulus of patch 140 in this alternative embodiment iseither compressible or has a resilient camming opening under the cammingaction of the electrode handle.

FIGS. 22-27 show an electrode remover according to one embodiment ofthis invention. Remover 200 is designed to work with the electrode andelectrode patch assembly described with respect to FIGS. 12-21 above. Itshould be understood that the principles of remover 200 may apply toother electrode designs as well.

Remover 200 has a housing 202 with an aperture 204 at its distal end. Anumber of previously undeployed electrodes 102 are stored within housing202. A pair of rails 214 and 216 hold the electrodes 102 in alignmentvia the electrode handles 107, as shown. While this embodiment of theremover is designed to provide sharps-safe removal and storage of aplurality of electrodes, the invention applies to removers designed toremove and store one or any number of electrodes.

As described above, electrodes for percutaneous electrical therapy areinserted through a patient's skin into underlying tissue with handleportions exposed above the skin. The first step in undeploying andremoving an inserted electrode is to line up the exposed handle 107 ofan electrode with the remover's aperture 204, as shown in FIG. 22, byplacing the distal face 205 of remover 200 against the patient's skin oragainst any portion of the electrode assembly (such as an adhesivepatch) surrounding the electrode. While not shown in FIGS. 22-27,aperture 204 is sized to surround an annular member (such as annularmember 141 shown in FIGS. 16 and 21 above) holding an electrode handleof an electrode assembly (such as that shown in FIGS. 13-22 above), thesharp point of which has been inserted through a patient's skin.

An electrode engagement fork 206 is pivotably attached to alongitudinally movable actuator 208 via an arm 209 and a hinged pivot210. A coil spring 212 biases actuator 208 upwards towards the actuatorand fork position shown in FIG. 28. A leaf spring 218 extends from arm209. A cross-bar 220 at the end of leaf spring 218 slides in groove 222and a corresponding groove (not shown) on the other side of housing 202.Leaf spring 218 is in its relaxed state in the position shown in FIG.22. In this position, a cross-bar 224 extending from the distal end ofarm 209 adjacent fork 206 lies at the top of a camming member 226 and acorresponding camming member (not shown) on the other side of housing202.

Downward movement of actuator 208 (in response, e.g., to pressure from auser's thumb) against the upward force of spring 212 moves cross-bar 224against a first camming surface 228 of camming member 226, as shown inFIG. 23. Camming surface 228 pushes cross-bar 224 of arm 209 against theaction of leaf spring 218 as actuator 208, arm 209 and fork 206 movedownward.

FIG. 24 shows the limit of the downward movement of fork 206. At thispoint, crossbar 224 clears the camming member 226, and leaf spring 218rotates fork 206 and arm 209 about pivot 210 to engage fork 206 withelectrode handle 107, as shown in FIG. 25. The tine spacing of fork 206is shorter than the diameter of the upper wide portion 112 of electrodehandle 107 but wider than the diameter of the narrow middle portion 113of electrode handle 107.

Release of actuator 208 by the user permits spring 212 to move actuator208, arm 209 and fork 206 proximally. The engagement between fork 206and electrode handle 107 causes the electrode to begin to moveproximally with the fork out of the patient and into the removerhousing, as shown in FIG. 26. At this point, cross-bar 224 is nowengaged with a second camming surface 230 of camming member 226. Cammingsurface 230 pushes cross-bar 224 against the action of leaf spring 218in the other direction (to the left in the view shown in FIG. 26) as theelectrode, fork and arm rise under the action of coil spring 212.

The electrode and fork continue to rise until they reach the upwardlimit of their permitted motion, as shown in FIG. 27. At this point,electrode handle 107 has engaged rails 214 and 216 and the most recentelectrode previously stored in remover 200. Electrode handle 107 pushesagainst the electrode handle of the previously stored electrode handle,which in turn pushes against any electrode handles stored above it inthe stack. In this manner, the latest electrode removed by remover 200goes into the bottom of the stack of used electrodes stored in remover200. Now that the sharp point 108 of electrode 102 is safely insidehousing 202, remover 200 can be withdrawn from the site on the patient'sskin through which the electrode had been inserted. Once cross-bar 224clears the top of camming member 226, and leaf spring 218 moves arm 209back to the center position shown in FIG. 22.

Modifications of the above embodiments of the invention will be apparentto those skilled in the art. For example, while the invention wasdescribed in the context of percutaneous electrical therapy in whichelectrodes are used to deliver electricity to a patient, the insertedelectrode holding features may be used with electrodes designed formedical monitoring and/or diagnosis. In addition, the inserted electrodeholding features of this invention may be used with acupuncture needlesor other needles not used for conducting electricity to or from apatient.

What is claimed is:
 1. A percutaneous electrical therapy systemcomprising: an electrode electrically connectable to the control unit,the electrode comprising a sharp point at a distal end configured to beinserted into a patient's tissue; and an inserted electrode holdingmechanism configured to hold the electrode in place after insertion ofthe sharp point of the electrode into the patient's tissue; wherein theinserted electrode holding mechanism comprises a holding elementconfigured to be attached to the patient and to the electrode, theholding element including a patch configured to mechanically interactwith at least a portion of the electrode.
 2. The system of claim 1wherein the patch comprises an aperture, and the inserted electrodeholding mechanism further comprises an electrode handle attached to theelectrode and configured to mechanically interact with the patchaperture.
 3. The system of claim 2 further comprising an introducerconfigured to insert the electrode through the patch aperture and tocause the electrode handle and the patch aperture to mechanicallyinteract.
 4. A percutaneous electrical therapy system comprising: anelectrode electrically connectable to the control unit, the electrodecomprising a sharp point at a distal end configured to be inserted intoa patient's tissue; and an inserted electrode holding mechanismconfigured to hold the electrode in place after insertion of the sharppoint of the electrode into the patient's tissue; wherein the insertedelectrode holding mechanism comprises a holding element configured to beattached to the patient and to the electrode; and wherein the insertedelectrode holding mechanism, the electrode and the holding element areincluded in an electrode assembly, the electrode assembly being operableto insert the electrode into the patient's tissue and being configuredto attach to the patient.
 5. The system of claim 4 wherein the electrodeassembly comprises a movable actuator configured to move the electrodefrom an uninserted position to an inserted position, and the insertedelectrode holding mechanism comprises an actuator holding mechanismconfigured to hold the actuator in place when the electrode is in itsinserted position.
 6. The system of claim 5 further comprising anactuator tool configured to move the actuator and the electrode from theuninserted position to the inserted position.
 7. The system of claim 6wherein the actuator tool is further configured to move the actuator andthe electrode from the inserted position to the uninserted position. 8.A percutaneous electrical therapy system comprising: an electrodeelectrically connectable to the control unit, the electrode comprising asharp point at a distal end configured to be inserted into a patient'stissue; an inserted electrode holding mechanism configured to hold theelectrode in place after insertion of the sharp point of the electrodeinto the patient's tissue; and a conductor connecting the electrode andthe control unit, wherein the inserted electrode holding mechanism isfurther configured to provide strain relief to the electrode.
 9. Amethod of providing electrical therapy comprising: inserting anelectrode into a patient; using an inserted electrode holding mechanismto hold the inserted electrode in place in the patient; and applying anelectrical signal to the electrode from a control unit; wherein theinserted electrode holding mechanism comprises a holding element, andthe method further comprises attaching the holding element to thepatient; wherein the holding element comprises a patch, and using aninserted electrode holding mechanism comprises mechanically interactingat least a portion of the electrode with the patch.
 10. A method ofproviding electrical therapy comprising: inserting an electrode into apatient; using an inserted electrode holding mechanism to hold theinserted electrode in place in the patient; and applying an electricalsignal to the electrode from a control unit; wherein the insertedelectrode holding mechanism comprises a holding element, the methodfurther comprising attaching the holding element to the patient; whereinthe holding element comprises a housing, and inserting an electrode intoa patient comprises moving the electrode within the housing.
 11. Themethod of claim 10 wherein inserting an electrode into a patientcomprises moving an actuator within the housing, and using an insertedelectrode holding mechanism comprises mechanically interacting theactuator with the housing to hold the inserted electrode in place in thepatient.